Correct path segment regex (microsoft#44149)

The old version incorrectly matched anything with a leading or trailing
slash.  The empty segment should only be detected between two slashes.

Author: amcasey

src/compiler/path.ts

@@ -658,7 +658,7 @@ namespace ts {
     //// Path Comparisons
 
     // check path for these segments: '', '.'. '..'
-    const relativePathSegmentRegExp = /(^|\/)\.{0,2}($|\/)/;
+    const relativePathSegmentRegExp = /(?:\/\/)|(?:^|\/)\.\.?(?:$|\/)/;
 
     function comparePathsWorker(a: string, b: string, componentComparer: (a: string, b: string) => Comparison) {
         if (a === b) return Comparison.EqualTo;